1. Field
One or more embodiments relate to an apparatus for detecting a position of a control rod, and more particularly, to an apparatus for precisely and easily detecting a position of a control rod that moves vertically.
2. Description of the Related Art
In a pressurized water nuclear reactor, a control element drive mechanism (CEDM) adjusts a reactivity of a reactor core by controlling a control rod to move vertically in the reactor core according to a control signal. Accordingly, position information of the control rod is very important in designing a reactor core protection system. In particular, for stability and reliability of all devices mounted in an integrated nuclear reactor, a CEDM or a position indicator of a control rod has to operate in very harsh environmental conditions in the integrated nuclear reactor.
In a conventional nuclear reactor, a position indicator including a reed switch is used to detect a position of a control rod. In general, the control rod is coupled to a lower end portion of a control rod driving shaft and vertically moves in a reactor core at the same time as the control rod driving shaft moves vertically. The reed switch is turned on/off by a permanent magnet mounted on an upper end of the control rod driving shaft.
As shown in FIG. 1, a reed switch 1 used in a conventional position indicator includes one pair of flexible magnetic bodies hermetically sealed in a glass tube 2 filled with inert gas. The reed switch 1 operates so that mechanical contact points are generally separated from each other and contact each other only when a magnetic field formed by a permanent magnet mounted on an upper end of a control rod driving shaft is applied to the reed switch 1. A plurality of the reed switches 1 are arranged on a non-magnetic plate 3, and a circuit is formed by connecting each of the plurality of reed switches 1 to a resistor. A structure and an operation of the reed switch 1 are well known, and thus, a detailed explanation thereof will not be given.
When the conventional position indicator using the reed switch 1 is employed, since the reed switches 1 are aligned, a resolution equal to or less than a length of the reed switches 1 may not be obtained. Thus, it is difficult to obtain precise position information required by a small nuclear reactor that operates by using a load following method.
Also, in an integrated nuclear reactor, the inside of an upper pressure vessel is filled with high-temperature primary water. A lot of efforts and attempts to secure or develop permanent magnets and reed switches that may withstand such high temperature are necessary.